Hi Joel et al.,
I had the same issue on Canon 5D Mark II and while looking for a solution hit a link to your question. Here are my findings to fix it.
I put in fully charged original Canon battery, checked with other cameras and with multimeter - it is in excellent condition and holds charge very well. Once I turn power on I see only battery sign flashing on top screen and nothing else happens. When I try switchers, buttons around the camera for some time the battery is not depleted - so there is no short circuit running. Interestingly when I open the battery compartment door with power ‘On’ and then close it with some pressure there is <1 sec blink on top screen of usual digits/parameters as it would be in usual working mode, but then it comes to an above described state. So I find the following issues to be checked, starting with ones mentioned earlier in the thread:
- Battery compartment door switch - it is tiny switch on the door that sometimes gets broken, another comment is describing how to check that. Be careful when playing with this switch, you can easily break it. I don’t think it will lead to blinking battery indicator, likely just won’t give you to switch the camera on.
- Maybe too obvious - try cleaning contacts, but if they are affected I would say you might have water damage and if it is inside battery compartment, it could be also on the power and main board.
- Another comment in this thread mentioned a data connector that is ‘supplying’ battery status information to main board - as of my experience even if you disconnect that cable it will just stop switching off when you open battery compartment door and doesn’t really block operation of the camera.
Now coming to the root of the problem in my case and something bit more complicated - power board plate / controller that is responsible to power supply from battery to all camera plates and components. It is located under top LCD screen and getting there requires taking out back and top covers - 5-10 mins when you know how to do it and 30 mins for the first time. This PCB contains several fuses to protect camera against short circuits and one of them had blown up. I had issue with ‘P’ fuse VD7-2291-001 that you can see on page 5 of Canon 5D Mark II Parts catalog C12-6201.
Easiest way to fix this is to replace the whole PCB part number CG2-2319-000 which will cost you around £30-60 itself or find and resolder the fuse impacted - which needs some good soldering experience as it is 2mm (SIC!) size fuse. You will need multimeter in ‘beep’ mode to test lettered fuses shown on the scheme - one or several might need a replacement. I am engineer by background, but never touched any of the above mentioned devices for more than a decade, so it was a new [re]learning experience and after some time spent on watching YouTube videos and looking for manuals and ordering fuses I managed to successfully resolder fuse in question and fix the issue. Looking back: if you are fixing only one camera I would strongly recommend just replacing the whole PCB. This will require only a screwdriver, new PCB and a pair of good hands.
I did the above mentioned exercise for one of 3 Canon 5D Mark II I bought specifically to play with their electronics and try fixing them. They had essentially same issue - please see description below that might help in your case:
Second camera was not switching on at all, simply no reaction. Issue was another ‘N’ fuse blown up on PCB, again either resolder it or replace PCB. Rest was working perfectly.
Third camera also was not switching on at all, but interestingly did show some signs of water damage - so when I opened it to check PCB, the board itself was perfectly working, but there was a corrosion sign on the data cable (CH1-8590 that you can see in manual mentioned above) connecting PCB to Main board. Corrosion affected one of copper connector threads breaking it for 1mm and thus not allowing to transfer signal. I cleaned the plate and affected areas with 45% phosphoric acid and after examining them replaced this connector, all the rest was working perfectly.
So at the end of the day looks like power board is the first suspect you need to check to fix power issue with Canon 5D cameras. Important conclusion from here - if your camera fell into water, first thing take out the battery ASAP and wither send it to service or open up to dry out boards, especially if it is salt water that will corrode all connections.
I hope this write-up is helpful. I am first time at this website and maybe will add step-by-step instructions with pictures as fully understand seeing how to do all this would be way more helpful.
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